by Jim Jennings
It doesn’t matter how efficient upstream processes are if grinding slows you down
Effective grinding involves removing the most metal in the shortest time, while not wearing the disc or burning out the grinding tool prematurely. Here are eight tips to help ensure your grinding operation is effective, productive, and free of workflow bottlenecks.
1. The Right Tool for the Right Job
Considering that grinding discs are consumable products, it is imperative shop operators use the right tool, at the right time, and for the right job. For example, if an application calls for between 8 and 10 amps, and the operator opts for an angle grinder rated for only 6 amps, this can represent issues when the tool needs to be replaced sooner than expected.
Opting to purchase higher quality tools rated for industrial work—rather than low-cost tools that wear out quickly—will serve organizations in the long run. This includes using high quality grinding discs and flap discs that work with right-angle grinders as a system, and ensuring operators use grinders that can handle adequate amperage for the task at hand.
2.Mind the Grind
An experienced operator can audibly determine if a grinding tool is working correctly. Effectively engaged, the grinder should emit a sound with a constant pitch. A lower pitch means the tool is being overworked; a higher pitch means more pressure can be applied. So listening to the pitch can make all the difference in ensuring grinding discs are being used productively and efficiently.
3. Work the Angles
For maximum efficiency, operators should ensure metal pieces are approached from the precise angle. Keeping in mind that grinding discs are intended to be used at a working angle of 15 to 20° from horizontal, the wear pattern on the disc face circumference should be about double the disc thickness. This means that if the wear pattern is 0.75 in. (I9 mm), for example, the approach is too flat, meaning too many of the grinding disc’s grains are being engaged at one time. If the disc is 0.25 in. (6.35 mm) thick, then a 0.5-in. (12.7 mm) wide wear pattern should be showing on the wheel; and if the pattern is only 0.25 in. (6.35 mm) wide, the angle of approach is too high.
4. Safety First
Using a grinder with a guard, or using appropriately powered tools seem like no-brainers, yet many operators continue to disregard OSHA protocols. While a guard can be a bother in some situations, opting not to use one can lead to serious personal injury.
Dropping the abrasive is another potential safety hazard and one of the most overlooked causes of abrasive failure. All too often, operators drop a disc, inspect it, and then put it on the grinder, only to have the disc fly apart. A disc that falls apart in a high rpm right-angle grinder can be dangerous. Simple steps such as unplugging tools while switching out abrasive media, or using tools such as file grinders when grinding in tight areas, can go a long way towards preventing OSHA fines and serious emergencies.
5.The Spark Test
While amp meters are useful in determining pressure—whether the tool operator is pushing too hard or not hard enough—they can be expensive for some shops. But every metal grinding application produces sparks, and the flow of those sparks can be read as a visual amp meter of sorts. How those sparks from the workpiece flow can tell you a lot about how effective the grinding really is. Look to achieve maximum sparks when grinding—sparks should consistently flow about 1 to 1.2 m (3 to 4 ft) away from the workpiece. This visual test can show that the grains on the grinding wheel are effectively removing excess weld metal.
6. Streamline Workflow
If a part will eventually be prepped for paint, you may use a large-grit grinding disc to knock down the weld, then a 60 or similar-grit abrasive to reduce the Ra, or the average scratch depth. The steps can be critical. Every scratch an abrasive disc places in the metal must subsequently be removed by a finer-grit, and if you jump from a very coarse disc all the way down to a fine-grit media, troubles can arise.
If you stop too early, you may not have given the grit time to remove the deep scratches put on by the coarse-grit disc. This can lead to paint not adhering to the surface, resulting in a part being sent back for rework.
Operators can streamline the grinding process with the right abrasive. Certain flap discs, for instance, may help reduce or eliminate additional finishing steps, depending on the application. A specific flap disc can remove weld metal at the same rate compared to a more conventional 36-grit grinding disc, delivering a final finish of a 60-grit material.
7. Keep up the Pressure
While grinding down a weld can be relatively straightforward, moving the disc forward and backward, how this pressure is applied is essential to avoid overheating and/or glazed grains. Constant pressure, backward and forward and not excessively hard or light, is a key to effective grinding. Just enough pressure should be used to let the disc’s grains do the work, but no more.
8. Evolve and Adapt
Grinding is fundamentally a machining operation, only the cutting edges and chips are smaller. Different grinding discs are designed for different metals much like different cutting tools are designed for different applications. Some welds in high-strength, abrasive resistant steels have been known to be ground down best with specialized discs that can “chisel” or “chew” away at the hard, high tensile weld metal. This kind of selection can be application-specific.
Jim Jennings is national training manager for Canada, Walter Surface Technologies.
